The 113th Congress won’t be sworn in until January, but it’s already making history on the religious-diversity front.

Hawaii Democrat Tulsi Gabbard scored a first as the first Hindu elected to Congress, while another Hawaii Democrat, Rep. Mazie Hirono, became the first Buddhist elected to the Senate. California Democrat Ami Bera became the only Unitarian Universalist member of Congress after winning his recount against Republican Rep. Daniel E. Lungren.

A “Faith on the Hill” study released Friday by the Pew Research Center’s Forum on Religion & Public Life found that the newly elected Congress may be the most ecumenical in U.S. history. At the same time, the 113th could be seen as the least devout, with 11 members reporting their religion as either “unaffiliated” or “don’t know/refused.”

The results shouldn’t come as a surprise, given that Congress tends to track the direction of American society, according to the report.

“This continues a gradual increase in religious diversity that mirrors trends in the country as a whole,” said the Pew report. “While Congress remains majority Protestant, the institution is far less so today than it was 50 years ago, when nearly three-quarters of the members belonged to Protestant denominations.”

In terms of the head count, the winner was the Catholic Church, whose members picked up five seats, increasing their percentage among lawmakers from 29.2 percent in the 112th Congress to 30.4 percent. Several races now undergoing recounts could also tilt Catholic.

Protestants continued to make up the majority of lawmakers, but their numbers declined from 307 in the previous Congress to 299, for 56.4 percent of the total. Every Protestant denomination listed saw its numbers decline or remain the same with the exception of Baptists, who added six members to jump from 12.7 to 14 percent of the Congress.

The biggest drop-off among the major religions was Judaism. Jewish lawmakers saw their numbers fall from 39 to 32, lowering their percentage from 7.3 to 6 percent of Congress. Most of those losses came as the result of retirements after five Jewish members declined to run for re-election.

Two Jewish Democrats lost their races: Nevada Rep. Shelley Berkley, whose Senate bid fell short, and California Rep. Howard L. Berman, who was defeated by fellow Jewish Democrat Brad Sherman after they were mapped into the same district.

The number of lawmakers who declined to list a religious affiliation grew from six to 11, or about 2 percent, a record high for Congress but far lower than the national average.

“Perhaps the greatest disparity … is between the percentage of U.S. adults and the percentage of members of Congress who do not identify with any particular religion,” said the Pew study. “About one in five U.S. adults describe themselves as atheist, agnostic or ‘nothing in particular’ — a group sometimes collectively called the ‘nones.’”

At the same time, the body’s only avowed atheist, Democratic Rep. Fortney Pete Stark, lost his bid for re-election in California. Some atheist groups initially described Rep.-elect Krysten Sinema, Arizona Democrat, as a “nontheist,” and she was identified in the Pew study as the first lawmaker to publicly describe her religion as “none.”

But her spokesman, Justin Unga, said in a postelection statement to the Religion News Service that she does not identify herself as an atheist.

“Krysten believes the terms nontheist, atheist or nonbeliever are not befitting of her life’s work or personal character,” Mr. Unga said. “She does not identify as any of the above.”

As with the previous Congress, there was a distinct denominational divide between Republicans and Democrats. Republicans made up 69.1 percent of the Protestants, compared with 42.5 percent for Democrats. Twelve of the 15 Mormon lawmakers were Republican.

Catholics tilted toward the Democratic side by a margin of 57 percent to 43 percent, while Jewish lawmakers were 97 percent Democrat, with House Majority Leader Eric Cantor once again listed as the sole Jewish Republican.

All other non-Christian denominations, such as Muslim and Hindu, were made up exclusively of Democrats, as were all lawmakers who declined to specify a religion.